In certain treatment procedures such as dialysis (hereinafter, this term and the term dialysis treatment each encompass peritoneal dialysis, ultrafiltration, hemodialysis, hemofiltration, Hemo-ultrafiltration, hemodiafiltration and the like) excess body fluid is removed from the patient's body. An accurate knowledge of the patient's hydration state before starting a treatment session is desirable for determining the most appropriate dialysis treatment, for controlling of the dialysis apparatus, and for determining and achieving the patient's post treatment target weight.
For example, peritoneal dialysis is often conducted by the patient alone at home and without being constantly monitored or supervised by medically trained staff. In fact, home peritoneal dialysis patients are seen by the dialysis staff in charge only every 4-12 weeks. Therefore, hydration state measurements made in a professional setting are made only every now and then. For that reason, it is particularly important for peritoneal dialysis to be provided with accurate methods and devices in order to easily determine by oneself the present hydration state between examinations that are carried out by the medical staff every 4-12 weeks.
There are some methods available to estimate the hydration state of a patient including assessment of weight changes, edema, jugular venous pressure, blood pressure, the measurement of hematocrit, of natriuretic peptides (ANP, Pro-BNP, and BNP), cyclic guanidine monophosphate (cGMP) and/or inferior vena cava diameter. These methods are not all clinically useful because of limited accuracy or practicability or both.
The estimation of the patient's hydration (also referred to as the patient's hydration state) before a dialysis treatment session using bio-impedance analysis can be a useful step toward revealing the patient's hydration status. Bio-impedance techniques measuring body fluid content are advantageous in that they are non-invasive, relatively cheap, generally easily to perform and reliable if carried out correctly. Further they can in theory be carried out by the patient himself and even without professional supervision. However, these clinical methods are still too cumbersome for some patients. Also, when carried out, the results depend strongly on how accurately the electrodes used for the bio-impedance measurement are placed by the patient. In practice, it has turned out that a number of patients are not capable of using the electrodes which have to be placed on both arms, one arm and one foot, both feet, or the like in the intended manner. In consequence, the results stemming from bio-impedance measurements—if carried out at all—and their interpretation can suffer remarkably.